The present invention relates to an apparatus for controlling a starting operation of a boiler.
In a boiler starting operation, after a preparatory operation has been accomplished, a fuel supply system is operated with a burner being ignited, to thereby start increasing of a pressure and a temperature of the boiler. In this case, it is necessary to suitably control the starting operation in order to prevent each part of the boiler from being overheated or to prevent parts, having a greater thickness, of the boiler from being subjected to an excessive thermal stress.
Disadvantages encountered in a conventional apparatus for controlling a starting operation of a boiler reside in the fact that it is difficult to set an optimum temperature and pressure increase pattern which refers to a starting state where the temperature and pressure increases are accomplished in a minimum period of time while suppressing a thermal stress generation in parts, having a greater thickness, of the boiler. The greater thickness portions which are most important in the boiler are, generally, an outlet header of a super heater and the system separator (or drum). Therefore, the optimum temperature and pressure increase pattern is intended to mean a state in which a change rate of the outlet steam temperature of the super heater which rate, hereinafter referred to as a temperature increase rate, effects a thermal stress of the outlet header of the super heater 5 and a change rate hereinafter referred to as a pressure increase rate, of the steam pressure which effects a thermal stress of the steam separator (or drum) through the saturated temperature change are maintained just below the change rate limits allowable in light of the suppression of the thermal stress generation.
In the conventional apparatus, the temperature increase rate and the pressure increase rate are regulated by setting of function generators and, in order to carry out such setting, it is necessary to determine the rates by repeating the starting tests of actual drums. This requires a number of steps and is troublesome. Further, in the case where the steam pressure at the ignition time (initial pressure) is different from the steam pressure at which the adjustment is carried out, the actual rates would be offset from the desired temperature and pressure increase rates. In order to prevent such offset from generating, the function generators are operated to set the temperature and pressure increase rates so that they do not exceed the limits in a starting state under any initial pressure and in any step of the temperature and pressure increase process. As a result, the obtained temperature and pressure increase pattern is considerably offset from the optimum temperature and pressure increase pattern, and the consumed starting period is rather longer than that according to the optimum temperature and pressure increase pattern.
Moreover, in a conventional apparatus for controlling a starting operation of a boiler, it is difficult to reduce the starting loss. More particularly, case where the starting operation is carried out in accordance with predetermined temperature and pressure increase rates, a combination among the fuel replenishment amount running through a fuel flow rate regulating valve, the opening degree of a super heater bypass valve and an opening degree of the turbine bypass valve is not determined to a sole combination. Namely, there may be a combination where a great amount of fuel is replenished to the burner of the boiler, whereas, a great amount of steam is bypassed by a super heater bypass valve and a turbine bypass valve, and there is another combination reverse to the former combination. In the various combinations, a three-factor combination where it is possible not only to maintain the given temperature and pressure increase rates but to reduce the opening degree of the fuel flow rate regulating valve to a minimum may lead to an operation where the starting loss is minimized for the same starting period. However, the conventional apparatus does not function to cooperate the super heater bypass valve, the turbine bypass valve and the fuel flow rate regulating valve with each other. Therefore, in order to reduce the starting loss, there is no method other than a method of independently adjusting an opening degree setter and the function generators. As a matter of fact, it is almost impossible to adjust these components in such a manner that the starting loss is kept at a minimum while maintaining the above-described optimum temperature and pressure increase rates.
Additionally in the conventional apparatus for controlling a starting operation of a boiler, even if the temperature and pressure increase pattern becomes abnormal due to a disturbance or the like, any modification copying with such abnormal operation is not performed. More particularly, although the temperature and pressure increase rates are important state factors by which a thermal stress of the greater thickness portions of the boiler is governed, the conventional apparatus has no method of measuring these factors. In the conventional apparatus, these factors are out of the control. For this reason, if the temperature and pressure increase rates deviate from a pattern planned in adjusting the opening degree setter and the function generators due to a distrubance or the like, it is impossible to modify the deviation. Therefore, also in view of this aspect, it is necessary to plan the temperature and pressure increase rates at somewhat lower levels upon adjusting the opening degree setter and the function generators while estimating a margin of the suppression of thermal stress generation. This is one of the hindering factors of the starting period reduction.
An object of the present invention is to provide a boiler starting operation controlling apparatus which is capable of accomplishing a starting operation of a boiler in a short period of time while suppressing a thermal stress generated in greater thickness portions of the boiler and which is capable of reducing a starting loss.
In order to attain the object, in accordance with the present invention a steam or temperature and a steam or vapor pressure are detected, a desired value of a steam temperature change rate and a desired value of a steam pressure change rate needed for suppression of a thermal stress of greater thickness portions of a boiler are calculated based upon the detected values, a desired pressure increase value, a desired temperature increase value, a limit for a saturated temperature change rate which is given by preset constant or function of signal respecting a thermal stress of steam separator, and a limit for a super heater outlet temperature change rate which is given by presetted constant or function of signal respecting a thermal stress of super heater outlet header, and means are provided for calculating the respective operational amounts of a super heater bypass valve, a turbine bypass valve and a fuel flow rate regulating valve based upon the respective desired values, the steam temperature and the steam pressure. The present invention is further characterized in that the operational amounts obtained through these calculations are compensated based upon the change rate of the steam temperature and the change rate of the steam pressure.